BIP-173: fix typo in "Created" date

Author: SomberNight

bip-0173.mediawiki

@@ -8,7 +8,7 @@
   Comments-URI: https://github.com/bitcoin/bips/wiki/Comments:BIP-0173
   Status: Draft
   Type: Informational
-  Created: 2016-03-20
+  Created: 2017-03-20
   License: BSD-2-Clause
   Replaces: 142
 </pre>